Is the defense of Human dignity possible for a merely secular government?

The telegraph journalist the Rev. George Pitcher quoted in length on his blog a sermon made recently by the Archbishop of Canterbury, where he mentioned, one should give Caesar what belongs to Caesar, and to God what belongs to God. And His Grace interpreted in a way that, while the Church should be obedient to the secular power, the secular power should also give God what belongs to God, that is His Image in us: the human dignity.

My thought is, the secular power is NOT obliged to give God what belongs to God (though in the U.K. it might be different, as the Anglicanism is still the religion of the State) because the state is becoming in great part of the developed world atheistic and even hostile to Christian ideas. While in the enlightenment the human dignity was developed to be an universal foundation for a "secular" state, whose power, like Hobbes exclaimed, was not given by God, but by the people, who gave up a part of their freedom to the Leviathan, for the sake of peace and order. But in substantial difference to the world after the WWII, the European world during the time of Enlightenment and long afterwards, had not abandoned its Christian culture and ethical values, though the state was eventually separated from the Church.

The human rights are a weak echo of the old Christian idea of imago Dei and the essential equality between persons. But without Christianity the human rights becomes only terms on papers, and are able to be manipulated by functionaries.

I am not for a theocratic State, not in the least sense. I am for a democracy, but not for a democracy led without any common cultural values. But today's world, they call it the multi-cultural, is a pluralistic world with so many competing and contradicting culture values between groups of its citizens. How is democracy possible? It is no wonder that the state is becoming more and more authoritarian because to achieve a consensus between its citizens is too difficult.

A secular state of today won't care for holding the human dignity upright anymore. The cultural foundation is gone. But for the Catholic Church, this situation is nothing new, our Church grew out of the suppressions by the Roman Emperor. And Pope Benedict wrote in his book "Jesus of Nazareth" that the first alliance between the Church and Constantin was a temptation which resembled the temptation of Jesus Christ through Satan, in the last attempt to seduce Jesus Christ into embracing the worldly power.

We Catholics should be prepared for a hostile time, while retaining the idea of democracy.